You sure it's the speedo sensor mate as mine packed up and it was the wiring had come lose just like all ur fillings when u ride them things
going to try that at weekend,b4 it went it was erratic showing various speeds up and down then went off cheers
Mine did the same thing was saying I was doing 117mph and alsorts then just went to 0 I messed about with the wires under the right hand side of the seat and one was very lose from the connector sorted that out and boom problem solved mate
It's easy mate I'll give you a hand if needs be just make sure you get the right part (I'll help you with that too if you're totally stumped)